Or just spend 2 Runes on Shadow Kill and save your mana. Summoning rat swarms is reasonably effective, but mana-hungry and a bit unreliable, since a lot of enemies can run away from the rats.
Originally Posted by factotum
It's probably more honest to call it high chaos and extremely high chaos, honestly. The differences are mostly in how people treat Corvo, it only makes any mechanical difference in the very last mission.
Originally Posted by Mordokai
Spoiler: Late game spoilers
On extremely high chaos, Samuel the boatman betrays you and fires a flare immediately after dropping you off on the island, permanently putting every enemy in the level on maximum alert state.
In terms of challenge runs, pairing Clean Hands with Ghost is not super challenging. Mostly they involve doing the same things, so there are really only a couple of points in the game that turning a Ghost run into a Clean Hands run as well makes it noticeably more difficult. As long as you never have anything to do with Granny Rags and thus can avoid the sticky situation I mentioned previously, doing both together is quite viable. What Clean Hands doesn't pair well with is Mostly Flesh and Steel. That one's damn hard to pull off without killing people occasionally thanks to your dramatically reduced options for mobility. I know some people who did all three at once. Madmen, all of them.
You can still get Low Chaos without difficulty while killing a few people here and there. You can kill every single one of your assassination targets, plus everyone you get a quest that involves attacking, and still be quite a bit below the threshold for Low Chaos. Honestly, considering how cruel most of the non-lethal eliminations for the targets are, killing them outright seems a bit like mercy. Alternatively, I know for a fact that as long as you kill absolutely nobody else, you can kill every single Weeper in the game and still get the Low Chaos ending. Food for thought.